Sidebars

Installation

You must add the following to your user.js file in your
Mozilla profile in order for the User Agent and Source Sidebars to work:

user_pref("signed.applets.codebase_principal_support", true);

Or you can automatically add this statement by installing the user.xpi.

This will allow sidebar scripts from this site to request increased
access to various aspects of the browser including cross domain
scripting and access to preferences. When a script needs elevated
access, it will ask for permission from you. You can grant
permission on a per use basis or grant the permission always.

You can download the entire
source of the sidebars and install them locally where you will not
have to be concerned about granting this permission to yourself.